Coordinated observations of the effect of consecutive HSS pulses on
relativistic electron enhancement
Abstract
During the second half of 2019, a series of recurring, moderate
geomagnetic storms (Dst ≈ - 70 nT) emerged after a sequence of
high-speed solar wind streams (Vsw ≥ 600 km/s) impacted the
magnetosphere. During one of these storms, intense substorm activity was
also recorded (SML ≈ - 2000 nT on August 31 and September 1), as well as
a longer-lasting solar wind pressure pulse. We investigate this series
of events, using particle measurements from three missions that recorded
significant enhancements of relativistic electron fluxes: the Van Allen
Probes, Arase and Galileo 207 & 215 satellites. We use both the flux
intensity and the phase space density (PSD) of electrons, along with
interplanetary parameters and information on ultra-low frequency (ULF)
and chorus wave activity for a detailed analysis of this event. Our
study demonstrates the importance of substorm injections, even during
moderate or weak geomagnetic storms. The presence of seed electrons at
L* = 4-5, in addition to intense ULF and chorus wave activity, seems to
result in very efficient electron acceleration to relativistic and
ultra-relativistic energies. This work has received funding from the
European Union’s Horizon 2020 research and innovation programme under
grant agreement No 870437 for the SafeSpace project.